Floating bookshelves, these are bookshelves I like. Looks like you could do this with an IKEA kitchen wall cabinet minus door and turned horizontal to mount. IDEA for narrow wall next to our kitchen wall

If you suggest to any library enthusiast or Dewey Decimal System devotee that they organize their books by hue, you might be risking bodily harm, but once you show them these photos of color-coded bookshelves, they'll warm up to the idea.